物理化学：化学电源

1、1,化学与材料科学学院 School of Chemistry and Material Science,Chemical Power Source,2,化学与材料科学学院 School of Chemistry and Material Science,Chemical Power Source,3,Chemical Power Source,化学与材料科学学院 School of Chemistry and Material Science,4,Introduction to Batteries,Battery terminology Primary and secondary batte

2、ries Cell voltage (open circuit) Positive and negative electrodes Cathode and anode Power energy and charge Battery cell module and pack Battery charge and discharge curves State of charge Depth of discharge Self discharge C rate Cycle life,化学与材料科学学院 School of Chemistry and Material Science,5,Primar

3、y and Secondary Batteries,Primary Battery: not rechargeable (dry cell) Battery is composed of Positive electrode Negative electrode Electrolyte Separator Current collectors,化学与材料科学学院 School of Chemistry and Material Science,6,Primary and Secondary Batteries,化学与材料科学学院 School of Chemistry and Material

4、 Science,7,Primary and Secondary Batteries,化学与材料科学学院 School of Chemistry and Material Science,Anode: Zn + 2OH- - 2e- Zn(OH)2 Cathode: MnO2 + H2O +1e- MnOOH + OH- aaaaaaaaa MnOOH + H2O +e- Mn(OH)2 + OH,8,Primary and Secondary Batteries,Secondary Battery : rechargeable,化学与材料科学学院 School of Chemistry an

5、d Material Science,Cathode (LiMexOy) LiCoO2 -utilized for commercial batteries LiNiO2, LiMn2O4-prospective,Anode (CLix,Lithium-ion battery,9,Primary and Secondary Batteries,Secondary Battery : rechargeable,化学与材料科学学院 School of Chemistry and Material Science,Picture from: T. Takamura / Solid State Ion

6、ics 152-153(2002)19,Nickel-Metal Hydride battery,Cathode: NiOOH + H2O - e- Ni(OH)2 + OH- Anode: MeH + OH- + e- Me + H2O,10,Primary and Secondary Batteries,Secondary Battery : rechargeable,化学与材料科学学院 School of Chemistry and Material Science,Lead-acid battery,11,How to Calculate Electromotive Force(EMF

7、,Use half cell reduction potentials （ 25 C) Electrode reaction E, V Electrode reaction E, V Li+ + e Li -3.01 Ni+2 + 2e Ni -0.23 Rb+ + e Rb -2.98 Sn+2 + 2e Sn -0.14 Cs+ + e Cs -2.92 Pb+2 + 2e Pb -0.13 K+ + e K -2.92 O2 + H2O + 2e HO2- + OH- -0.08 Ba+2 + 2e Ba -2.92 D+ + e 1/2D2 -0.003 Sr+2 + 2e Sr -2

8、.89 H+ + e 1/2H2 0.00 Ca+2 + 2e Ca -2.84 HgO + H2O + 2e Hg + 2OH- 0.10 Na+ + e Na -2.71 CuCl + e Cu + Cl- 0.14 Mg(OH)2 +2e Mg + 2OH- -2.69 AgCl + e Ag + Cl- 0.22 Mg+2 + 2e Mg -2.38 Cu+2 + 2e Cu 0.34 Al(OH)3 + 3e Al + 3OH- -2.34 Ag2O + H2O + 2e 2Ag + 2OH- 0.35 Ti+2 + 2e Ti -1.75 1/2O2 + H2O + 2e 2OH-

9、 0.40 Be+2 + 2e Be -1.70 NiOOH + H2O + e Ni(OH)2 + OH- 0.45 Al+3 + 3e Al -1.66 Cu+ + e Cu 0.52 Zn(OH)2 + 2e Zn + 2OH- -1.25 I2 + 2e 2I- 0.54 Mn+2 + 2e Mn -1.05 2AgO + H2O + 2e Ag2O + 2OH- 0.57 Fe(OH)2 + 2e Fe + 2OH- -0.88 Hg+2 + 2e Hg 0.80 2H2O + 2e H2 + 2OH- -0.83 Ag+ + e Ag 0.80 Cd(OH)2 + 2e Cd +

10、2OH- -0.81 Pd+2 + 2e Pd 0.83 Zn+2 + 2e Zn -0.76 Ir+3 + 3e Ir 1.00 Ni(OH)2 + 2e Ni + 2OH- -0.72 Br2 + 2e 2Br- 1.07 Ga+3 + 3e Ga -0.52 O2 + 4H+ + 4e 2H2O 1.23 S + 2e S-2 -0.48 MnO2 + 4H+ + 2e Mn+2 + 2H2O 1.23 Fe+2 + 2e Fe -0.44 Cl2 + 2e 2Cl- 1.36 Cd+2 + 2e Cd -0.40 PbO2 + 4H+ + 2e Pb+2 + 2H2O 1.46 PbS

11、O4 + 2e Pb + SO4-2 -0.36 PbO2 + SO4-2 + 4H+ + 2e In+3 + 3e In -0.34 PbSO4 + 2H2O 1.69 Tl+ + e Tl -0.34 F2 + 2e 2F- 2.87 Co+2 +2e Co -0.27,化学与材料科学学院 School of Chemistry and Material Science,12,Examples,Calculate EMF of hydrogen fuel cell (with hydrogen and oxygen electrodes) O2 + 4H+ + 4e 2H2O 1.23 V

12、 H+ + e 1/2H2 0.00 V E = 1.23 0 = 1.23 V Calculate EMF of lithium fluorine battery F2 + 2e 2F- 2.87 V Li+ + e Li -3.01 V E = 2.87 (3.01) = 5.88 V,化学与材料科学学院 School of Chemistry and Material Science,13,High Voltage Batteries,化学与材料科学学院 School of Chemistry and Material Science,Strong reducing agent,Stro

13、ng oxidants,14,Open Circuit Cell Voltage,Cell open circuit voltage EocV EMF Positive electrode: Cu Negative electrode: Zn E+ = 0.34 V E- = -0.76 V E = 0.34 (- 0.76) = 1.1 V,化学与材料科学学院 School of Chemistry and Material Science,15,Cathode and Anode,Cathode: the electrode where reduction reaction takes p

14、lace Anode: the electrode where oxidation reaction takes place Secondary battery During charge Negative electrode is the cathode Positive electrode is the anode During discharge Positive electrode is the cathode Negative electrode is the anode,化学与材料科学学院 School of Chemistry and Material Science,16,Po

15、wer Energy and Charge,Power: 1 W (watt) = 1 V (volt) * 1 A (ampere) Charge : 1 Ah = 1 A * 1 h 1 Ah = 3600 C (coulombs) 1 C = 1 As = 1 A * 1 s,化学与材料科学学院 School of Chemistry and Material Science,17,Power Energy and Charge,Energy : 1 Wh (watt-hour) = 1 W * 1 h (hour) 1 Wh = 3600 J (joules) 1 J = 1 Ws (

16、watt-sec) = 1 V * 1 A * 1 s = 1 V * 1 C,化学与材料科学学院 School of Chemistry and Material Science,18,Power Energy and Charge,Specific power: power withdrawn per unit battery weight W/kg Power density: power withdrawn per unit battery volume W/L Specific energy : energy stored per unit battery weight Wh/kg

17、Energy density: energy stored per unit battery volume Wh/L,化学与材料科学学院 School of Chemistry and Material Science,19,Cell Module and Pack,Battery Cell (up to 4 V) Battery Module: several battery cells connected in series Battery Pack: several modules connected in series or parallel,化学与材料科学学院 School of C

18、hemistry and Material Science,20,Cell Module and Pack,化学与材料科学学院 School of Chemistry and Material Science,21,Introduction to Batteries,Battery terminology（电池术语） Primary and secondary batteries（一次与二次电池） Cell voltage (open circuit) (电压） Positive and negative electrodes（正电极，负电极） Cathode and anode（阳极，阴极）

19、 Power energy and charge（力量，能量，电量） Battery cell module and pack（电池与组装） Battery charge and discharge curves State of charge（充电状态） Depth of discharge（放电深度） Self discharge（自动放电或漏电） C rate（C 放电速率） Cycle life（循环寿命,化学与材料科学学院 School of Chemistry and Material Science,22,Charge and Discharge Curves,化学与材料科学学院

20、 School of Chemistry and Material Science,23,Charge and Discharge Curves,Charge voltage is higher than Eocv Discharge voltage is lower than Eocv Energy efficiency = (voltaic efficiency) * (coulombic efficiency) 1 The voltage drop is caused by cell resistance E = Eocv Edis = I R (cell resistance,化学与材

21、料科学学院 School of Chemistry and Material Science,24,Battery Component Resistance,Nickel metal hydride electric vehicle battery (300 W/kg,化学与材料科学学院 School of Chemistry and Material Science,25,Charge and Discharge,State of charge (SOC, %) Depth of discharge (DOD, %) SOC + DOD = 100 Self discharge Discha

22、rge “C” rate 1C, 2C, 1/2C,化学与材料科学学院 School of Chemistry and Material Science,26,Examples,A battery delivers its full capacity (50 Ah) at an average discharge voltage of 6 V. Full recharge of this battery at 7.5 V (average charge voltage) requires 6 hours with a constant charge current of 10 A. What

23、is the charge-discharge voltaic, coulombic, and energy efficiency of the battery? Voltaic efficiency = 6 V 7.5 V = 80% Coulombic efficiency = 50 Ah 60 Ah = 83.3% Total efficiency = 80% x 83.3% = 67% A battery module (15 kg) is fully discharged at a constant current of 30 A in 3 hours with an average

24、 discharge voltage of 12 V. What is the discharge energy? What is the specific energy? What is the C rate for this 3 hour discharge? Discharge energy = 12 V x 30 A x 3 hours = 1080 Wh Specific energy = 1080 Wh 15 kg = 72 Wh/kg C rate = 1/3 C What depth of discharge (%DOD) is equivalent to 30% state

25、of charge? What state of charge (% SOC) is equivalent to 80% depth of discharge,化学与材料科学学院 School of Chemistry and Material Science,27,Introduction to Batteries,Battery terminology Primary and secondary batteries Cell voltage (open circuit) Positive and negative electrodes Cathode and anode Power ene

26、rgy and charge Battery cell module and pack Battery charge and discharge curves State of charge Depth of discharge Self discharge C rate Cycle life,化学与材料科学学院 School of Chemistry and Material Science,28,Cycle Life,Cycle life is the number of charge-discharge cycles a battery can deliver (has to meet

27、energy and power performance targets) Cycle life depends on depth of discharge and temperature Examples lead acid battery nickel cadmium battery lithium ion battery,化学与材料科学学院 School of Chemistry and Material Science,29,Chemical Equilibrium and Kinetics in Batteries,Thermodynamics theories (chemical

28、equilibrium in batteries) Theoretical and practical specific energy of batteries Kinetics in batteries Equivalent circuit and models,化学与材料科学学院 School of Chemistry and Material Science,30,Thermodynamics Theories(During Discharge,化学与材料科学学院 School of Chemistry and Material Science,Chemical reactions du

29、ring “discharge”: Zn + Cu+2 Zn+2 + Cu,G = H - T S G: Free energy change from reactants to products (J/mole) negative H: Enthalpy change from reactants to products (J/mole) S: Entropy change from reactants to products (J/moleK,31,Example of Entropy Changes,化学与材料科学学院 School of Chemistry and Material S

30、cience,32,Thermodynamics Theories,electric work) z: Number of electron transferred F: Faradays constant (96500 C/mole) E: Electromotive Force (V,化学与材料科学学院 School of Chemistry and Material Science,33,Chemical Equilibrium and Kinetics in Batteries,Thermodynamics theories(chemical equilibrium in batter

31、ies) Theoretical and practical specific energy of batteries Kinetics in batteries Equivalent circuit and models,化学与材料科学学院 School of Chemistry and Material Science,34,Theoretical Specific Energy,Zn-AgCl Battery Overall reaction during discharge Zn + 2AgCl Zn+2 + 2Ag + 2Cl- Free energy change (G) duri

32、ng discharge G = -nFE = -189 kJ/mole = -52.5 Wh/mole Total weight of reactants Zn: 65 grams/mole AgCl: 108 + 35.5 = 143.5 grams/mole Total weight: 65 + 2*143.5 = 352 g = 0.352 kg/mole Theoretical specific energy 52.5 / 0.352 = 149 Wh/kg,化学与材料科学学院 School of Chemistry and Material Science,35,Theoretic

33、al Specific Energy,LI-F2 Battery Overall reaction during discharge 2Li + F2 2Li+ + 2F- Free energy change (G) during discharge G = -nFE = -nF(5.88) = -1135 kJ/mole = -315 Wh/mole Total weight of reactants Li: 7 grams/mole F: 19 grams/mole Total weight: 52 grams = 0.052 kg/mole Theoretical specific e

34、nergy 315/0.052 = 6062 Wh/kg,化学与材料科学学院 School of Chemistry and Material Science,36,Practical Specific Energy,Practical specific energy of a battery is significantly lower than the theoretical value (30%) Lower discharge voltage Activation polarization losses (kinetic losses) Ohmic losses Concentrati

35、on polarization losses Extra material weight Current collectors Terminals Battery case Separators,化学与材料科学学院 School of Chemistry and Material Science,37,Extra Materials,Battery current collectors and terminals Collect current from electrodes and interconnect to next battery cells Use materials with h

36、igh electric conductivity and good heat transfer coefficient Battery case Contain all battery components Use materials inert with electrolyte and electrodes Need safety release valve with sealed cells Separator Separate positive and negative electrodes (prevent short circuit) Made of insulating mate

37、rials with high porosity,化学与材料科学学院 School of Chemistry and Material Science,38,Chemical Equilibrium and Kinetics in Batteries,Thermodynamics theories (chemical equilibrium in batteries) Theoretical and practical specific energy of batteries Kinetics in batteries Equivalent circuit and models,化学与材料科学

38、学院 School of Chemistry and Material Science,39,Kinetics in Batteries,Source of voltage losses Electrode activation polarization losses Butler-Volmer equation Depends on electrode reactions Ohmic losses Ohms law Electronic resistance (electrode current collector, tabs. And terminals) Ionic resistance

39、 (electrolyte and separator) Temperature effects Concentration polarization losses Nernst equation Depends on diffusion in electrolyte and solid state,化学与材料科学学院 School of Chemistry and Material Science,40,Activation Polarization Losses ( Butler-Volmer,Current density i is a function of: : Activation

40、 polarization loss (overpotential) i0 : Exchange current density : The symmetry factor F : Faradays constant R : Molar gas constant T : Temperature,化学与材料科学学院 School of Chemistry and Material Science,41,Activation Polarization Losses ( Butler-Volmer,Overpotential During discharge Negative electrode (

41、anode) - = E-dis E- (table) or E-dis = E- + - - positive value Positive electrode (cathode) + = E+dis E+ (table) or E+dis = E+ + + + negative value Discharge voltage = E+dis - E-dis = (E+ - E-)+ (+ -,化学与材料科学学院 School of Chemistry and Material Science,Anodic,Cathodic,42,Activation Polarization Losses

42、,化学与材料科学学院 School of Chemistry and Material Science,43,Effect of Rate on Discharge,化学与材料科学学院 School of Chemistry and Material Science,44,Concentration Polarization Losses (Nernst Equation,化学与材料科学学院 School of Chemistry and Material Science,Reaction for electrode A aA + ne bB Cell reaction is (n/2) H2

43、 + aA bB + nH+ Nernst equation A : Concentration of reactant B : Concentration of product R : Molar gas constant T : Temperature F : Faradays constant,45,Activation and Concentration Polarization Losses,化学与材料科学学院 School of Chemistry and Material Science,Activation polarization losses Discharge volta

44、ge = E+dis - E-dis = (E+ - E-)+ (+ - -) = Eoc, table + (+ - -) Concentration polarization losses Activation and concentration polarization losses Discharge voltage = Eoc,real + (+ -,46,Total Voltage Losses,化学与材料科学学院 School of Chemistry and Material Science,Total voltage losses （extrinsic）= Activatio

45、n losses + Ohmic losses + Concentration losses,47,Chemical Equilibrium and Kinetics in Batteries,Thermodynamics theories (chemical equilibrium in batteries Theoretical and practical specific energy of batteries Kinetics in batteries Equivalent circuit and models,化学与材料科学学院 School of Chemistry and Mat

46、erial Science,48,Equivalent Circuit,Equivalent circuit is composed of resistors (measured or calculated) representing R+ (positive side) = (Re+ + Rc+ + Rt+) Re+: Positive electrode (activation and concentration losses)* Rc+: Positive current collector (Ohmic loss, electronic) Rt+: Positive tab and t

47、erminal (Ohmic loss, electronic) Separator Rsep: Electrolyte in separator pores (Ohmicl loss, ionic) R- (negative side) = (Re- + Rc- + Rt-) Re-: Negative electrode (activation and concentration losses)* Rc-: Negative current collector (Ohmic loss, electronic) Rt-: Negative tab and terminal (Ohmic lo

48、ss, electronic) Total voltage losses is equal to IRtotal,化学与材料科学学院 School of Chemistry and Material Science,49,Models for Calculating the Resistance in Battery Components,Model for tabs and terminals (Ohmic loss) Ohms law: across a plate R = * L / A Where is resistivity (Ohm-cm) FEA for current coll

49、ectors (Ohmic loss) Porous electrode theory for electrodes (activation and concentration losses,化学与材料科学学院 School of Chemistry and Material Science,50,Models: FEA and Porous Electrode Theory,FEA for current collector Ohms law Porous electrode theory Butler-Volmer equation Ohms law,化学与材料科学学院 School of

50、 Chemistry and Material Science,51,Equivalent Circuit for Batteries,Multi positive electrodes in a cell are in parallel 1/Re+total = 1/Re+ + 1/Re+ + 1/Re+ Re+total = Re+ / 3 (or Re+total = Re+ / n) Multi negative electrodes in a cell are in parallel Re-total = Re- / 3 (or Re-total = Re- / 3,化学与材料科学学

51、院 School of Chemistry and Material Science,For a battery cell Power = f (1/R) R = f (1/surface area,52,Specific Energy VS Power,化学与材料科学学院 School of Chemistry and Material Science,53,Specific Energy VS Power,化学与材料科学学院 School of Chemistry and Material Science,54,Estimate Cell Voltage During Discharge,

52、化学与材料科学学院 School of Chemistry and Material Science,55,Estimate Heat Generation,化学与材料科学学院 School of Chemistry and Material Science,Entropic heating (or cooling) TS = T * nF * (dE/dT) (intrinsic) Heat generation by Ohmic losses Rate of heat generation = I2 * Rtotal (can be minimized by engineering design) Rtotal = dE/dI Heat generation by overcharge,56,Discharge Model for the L